Power requirements for stackable switches are becoming more unpredictable. As a result, the old method of having a dedicated power supply for each stackable switch is becoming less cost effective and does not provide the reliability of power sharing and redundancy. Stackable switches have their own integral power supply that is designed to meet the needs of only that one device's switching circuitry and to provide power via its Power Over Ethernet (PoE) ports. Some variations, such as the DecHub 90 & 900, had snap-on power supplies that converted a hub module into a stackable module. Although stackable switches have the capability to connect into a Redundant Power Supply (RPS) via a dedicated RPS connector and cable, these solutions only provide power; they do not provide power-sharing from one switch to another. Furthermore, they use dedicated connectors to provide the power to the switch.
There is a catch-22 problem managing power allocation between switch port operation and PoE power delivery. If one were to first measure the power used by the switching circuitry to estimate the amount of power the circuitry will need, the estimate will be low because the circuitry is in an idle state and therefore not consuming as much power as when it is passing data in an active state. If one were then to allocate PoE power based on this low estimate and then turn on the external devices, the devices would begin to transmit data, thereby activating the switching circuitry, which would not receive sufficient power. On the other hand, if one first tries to allocate all the PoE power requested, insufficient power may be reserved for the switching circuitry. To avoid such problems, existing switches typically supply the maximum (worst-case) power to the switching circuitry and to PoE at all times.
What is needed, therefore, are improved techniques for providing power to network switches.